The purpose of this project is to develop theory for the interpretation of biomedical and chemical measurement techniques. At present we are working on optical spectroscopy applied to estimate optical tissue parameters to distinguish between normal and abnormal tissues. The project deals with the theory of optical measurements as used to estimate optical properties of human tissue. The main subject under investigation at present is that of determining the effects of anisotropic optical parameters on measurements made in the time-gated mode, that is, when light intensities induced by a laser source irradiating tissue are measured as a function of time, rather than of the light intensity from a continuous beam measured as a function of the distance between the source and the detector. We have developed a mathematical formalism to solve problems in media whose optical parameters are anisotropic with respect to a slab geometry model, and using this model indicated how to estimate the angles that characterize the anisotropy from measurements of the light intensity as a function of time.